How Many Miles do Semi Trucks Last?
This question has been around for a long time. Also, why do diesel trucks last longer than gas trucks? Another question that frequently pops up is why do semi-diesel trucks last so long?
I have a Ford F-250 7.3 Diesel Truck, not exactly a semi but it feels like it sometimes to this author. A lot of research was done by me on which truck to buy and which motor was the best. There was a phrase I came across frequently.
“A 7.3 is a go but a 6.0 is a no.”
I’ve heard this from many mechanics and found out that the 7.3 was nicknamed the ‘Million Mile Motor’ but on the other hand when I visited forums to come up with ‘Hands-On’ real research data everyone says that they have 500,000 to 600,0000 miles but they go through 3 or 4 transmissions also. Long story short, I bought the 7.3 and plan to ‘chip it’ to prolong the life of the transmission as long as possible. In my younger years, I would have ‘chipped it’ to gain horsepower and speed. I guess I’m getting old…
Unfortunately, the 7.3 is no longer available.
According to Commerce Express, a semi will last 750,000 to 1,000,000 miles and the average truck driver drives about 45,000 miles per year.
When talking to drivers on forums they consider 500,000 miles to be the (bragging) ‘breaking in’ point for semis and there are bragging rights of owning semis that last 1.5 million miles and even 4 million miles.
In reality, the “Break in” on a large-bore diesel engine is done at approximately 50,000 miles. That’s when you will see your MPG increase. A diesel engine can go a lot more miles than 500,000 miles. That’s just when the big trucking companies trade them in before all the other components start failing.
With that many miles, it is not surprising that semis get frequent maintenance! These statistics are about the same everywhere else I looked online. So according to these statistics, the average semi lasts 15 to 16 years. If you are an owner-operator take these stats into consideration when purchasing your next semi. Did you know that US Special Delivery is hiring drivers?
Also, the national average is that the trucking companies swap out their semis every 4 years or 500,000 miles (as mentioned above). That is why there are so many semis out there for sale with about that mileage. It has been said that 500,000 miles is the breaking-in point and it also has been said that the 500,000-mile mark is when the semi will start to nickel and dime you to death. But we know the truth now, don’t we? 50,000 miles is the true breaking in mileage and despite the fact that components start to fail they still last much longer than 500,000 miles!
“US Special Delivery keeps excellent maintenance on their vehicles and that is why they last much longer.”
So why do diesel trucks last so long? Especially semis?
I have a friend that is a semi-driver and every weekend he is working on his truck. So is frequent maintenance the key? Another semi-driver tells me that they leave the engine running which keeps the oil in the motor instead of frequent start-ups with the oil in the oil pan. I read an article once that told me the worst time for your car is start-up cold because all of the oil is in the oil pan instead of the engine which causes more wear and tear. So his theory sounds plausible as well. But, when I conversed with the Fleet Director Mark Deskis he informed me that excessive engine idling KILLS a diesel engine. It is in a fuel situation at idle to run and will now plug up the DPF (diesel particulate filter). That’s why real over-the-roaders use an APU (accelerated processing unit) now. A good-grade engine oil will allow proper lubrication at startup.
Yet, another mechanic told me that semis were just built that way. Well, the same thing is true for smaller truck diesel as well.
Time to do some research and find out the truth!
Use, Fuel, and Design are the main contributors to semi-diesels lasting longer.
Use
Diesel engines run longer with fewer start-ups when compared to gasoline engines which promote less wear and tear. Starting up an engine frequently (with the oil in the oil pan) contributes to more wear-and-tear to gasoline motors and few starts and stops also help get more mileage out of the motor.
Fuel
The difference between diesel fuel and gas is said to make diesel engines last much longer. Jokingly, the two guys at Car Talk talk about diesel fuel basically as being the dirtiest fuel (less refined) than gas and say they pump it out of the ground and put it straight into your engine. But this isn’t true according to US Special Delivery’s Fleet Manager Mark Deskis.
“Diesel fuel is just as refined, if not more than gasoline is. It has to be ultra low sulfur due to our buddies at the EPA which robbed the fuel of needed lubrication. Lubrication additives are used now, clearance tolerances are much closer in a diesel’s fuel system now compared to the days of the old mechanical pumps.”
Gas is flammable while diesel is labeled as combustible and not flammable. Plus gasoline burns off quickly while diesel does not and diesel fuel contains about 30% more energy than gasoline.
However, it is known that diesel fuel lubricates the engine better than gas which lessens the wear and tear of critical engine components like the pistons. It also helps improve oil flow and makes the engine run more smoothly.
Wait, run more smoothly? Why does it always sound like it’s knocking and so loud then? The diesel motor is pressurized and works off of a pressure mechanism to make it so loud. The “knock” you hear from a diesel engine is due to it being a compression ignition. This brings me to the next point, design. Why do they have to be made superior?
Design
Diesel engines have less wear and tear due to them having lower RPMs. One of the first things I noticed when I bought my first diesel is the low numbers on the tachometer. The lower the revolutions per minute (RPM) the less wear-and-tear occurs on the motor.
All diesel engines are compression ignition, not spark ignition. They have a much higher thermal efficiency than gasoline, meaning they get a lot more power to the wheels per gallon of fuel burned. That allows them to turn at a much lower RPM, creating less wear.
Size Matters
When I was young I looked at a straight-six cylinder semi motor that was an older Cummins NTC-350 that had 855 cubic inches. This blew my mind when I was young because that was a lot of cubic inches for a straight 6. The larger engine parts contribute to better oil flow within the motor.
With a larger size comes more oil. Types of diesel typically hold 10 times more oil in the engine than regular-sized gasoline motors which provide less oil in the oil pan.
Another reason why diesel engines last longer than gas engines is that the engines of diesel are gear-based which means they will typically keep going if something happens and it is only after one catastrophic failure or multiple failures that the diesel motor will stop functioning.
What happens when the thermostat in your car starts sticking? That’s right! The engine overheats! Semi-motors have multiple thermostats to help keep them from overheating. With a gasoline car, you have to pull over right away.
Basically, it has been known that semis have to have fewer break-downs and last longer so designers put in checks and balances within the motor to help keep that from happening. In short, diesel motors are designed better.
Conclusion:
The reason why semis last longer and can have high mileage is due to three factors. Use, Fuel, and Design.
If you are interested in becoming a driver or having us deliver a load for you please feel free to contact US!
The article was written by Michael Rock of The Internet Presence, LLC, and US Special Delivery is the source.